A wall plug anchor assembly of this type has been described, for example, in German Laid-Open Patent Publication No. 36 03 134.
In the known dowel, the sleeve body is provided by a thin-walled piece of pipe or tubing, and the head end is fashioned by a conically or outwardly flared portion. At least two diametrically arranged slots extend from the tail or foot end of this wall plug anchor assembly and thence substantially over the full length of the sleeve body.
The particular body which serves to spread or flare the legs outwardly is a sphere which is positioned at or in the tail end, i.e. the end opposite the flared end or crown of the dowel. This sphere has a diameter which is greater than the inner diameter of the sleeve body.
The known tubular wall plug anchor assembly can easily be driven, i.e. without pre-drilling of holes, into the wall material, such as gas-expanded, expanded or foam concrete, light concrete and the like as may be used in pre-formed products, such as bricks, blocks, or plates made of such concrete material.
During the driving-in process, the sphere is pressed in rearward direction towards the head and, consequently, the legs of the sleeve body are spread apart or flared and create an anchoring effect in the surrounding material.
The positive anchoring effect achieved by the flared sleeve portions of the known tubular wall plug anchor assembly during the spreading movement of the sphere is for most purposes sufficient. However, it has been found that the penetration or advance of the sphere, which acts as the spreading or widening body, is not always uniform, and is predominantly a function of the density of the material into which the wall plug anchor assembly is driven.
In the case of a relative high density of the gas-expanded or light concrete or like material, a larger penetration is achieved as well as a wider angle or flaring of the sleeve portions or legs. In the case of a lesser density one can achieve only a lesser penetration with the body causing the spreading, i.e. the sphere, in the slotted longitudinal section of the sleeve. Accordingly, a lesser degree of spreading of the respective legs is experienced.
DE-OS No. 36 03 134 accordingly suggests that in order to achieve the optimum penetration depth of the spreading body into the slotted portion of the sleeve, independently of the density of the surrounding material into which the wall plug anchor assembly is to be driven, the sphere, or in its place a spreading cone, be furnished with a female screw-thread. Into this is then screwed the male or exterior screw-thread on the shaft of a screw or bolt which acts as support element and which includes a head which can abut as a shoulder or annular support against the head end of the tubular portion of the dowel.
Thus, the known wall plug anchor assembly can be forced or driven substantially directly into the gas-expanded or light concrete and the like material, by directly applying hammer strokes on the head of the bolt which serves as the support element, initially without any flaring of the leg portions. Subsequently, by turning of the bolt, the spreading body, i.e. the sphere or the spreading cone in its place, is advanced in, or pulled into, the slotted region of the sleeve body, and this is then spread or flared to the desired extent to attain the desired anchoring effort.
One disadvantage of a tubular wall plug anchor assembly according to this prior art, however, arises from the subsequently additionally required turning action for moving the bolt, following the required actual driving-in or penetration action, to advance in the concrete material that is at hand to anchor the dowel.